SpaceEngine is not based on Celestia nor any other engine, I wrote the code all by myself (except some common algorithms like quicksort, memory manager, OpenGL tricks, that can be found in books and everywhere else in the Internet). The first public version was 0.74, it was released on the Russian GameDev forum. It worked only on NVidia GPU, has procedural planets, but no procedural terrain (3D terrain was only on Earth and some other Solar System bodies). You can follow SE evolution on the Russian GameDev (Google translate could help):

Until 0.74, SE had a very quick version number change, every small improvement increased the number by 0.1: 0.5 - 0.6 - 0.7. Then I realized that it is too fast, so I decreased the numerical step and now every big release has a version number increased by 0.0.1, while patches add 0.0.0.1: 0.9.6.0 - 0.9.6.1 - 0.9.6.2

Terrain engine in SE is pretty much the same even now, it wasn't changed since a beginning of SE.

Absolutely awesome! I run 0.85 (patch) version with r_IgnoreFBO enabled and I can run the Space Engine on Intel Graphics Media Accelerator 4500MHD without graphics glitches (apart from it making only a few frames per second)! Perfect! (see attached images)

Yesterday I've tried SE 0.9.4 (I had it in my external HD), and I discovered I couldn't see procedural terrain, planets were all white. But it was an already implemented feature, right? I didn't investigated very much, also because it was 11 pm!

The universe is not required to be in perfect harmony with human ambition.